The purpose of parts of the preceding discussions concerning
various past experiments was to emphasize that truly reliable data
concerning the diffuse ultraviolet background are hard to come by.
In particular, one cannot simply accept data as they are presented;
one must look very critically at the circumstances under which they
were obtained to judge the likelihood that the data deserve serious
attention. Consider now four additional data sets.

5.7.1 OAO-2 The pioneers of the study of diffuse
ultraviolet background radiation were Lillie & Witt
(62), and their
conclusions
concerning the ultraviolet albedo a and the scattering parameter g,
for interstellar grains are still widely used. My concerns
(33) about
their data have centered on the extremely small (8.5 x 10-6
sr) OAO-2 field of view, and the time-variable dark current due
to low Earth
orbit through the radiation belts. The OAO-2 was intended for the
study of point sources, not low-surface-brightness extended
backgrounds. Such experiments, in low Earth orbit, are prone to
problems of false patchy backgrounds, and a patchy background is
exactly what Lillie & Witt report. In view of this their conclusions
must be confirmed by other experiments that are optimized for the
study of diffuse backgrounds rather than point sources.

5.7.2 BERKELEY ARIES ROCKET
Jakobsen et al
(53) made rocket
measurements, at altitudes below 250 km and with broad-band
photometers, of a region at constant galactic latitude but having
spatially variable hydrogen column density. Intensities of 600 to
3000 units are reported, and correlations, of varying strength, of
intensity with column density, are reported at all three wavelengths
(1590, 1710, and 2135 Å) observed. Murthy, Henry & Holberg
(83)
have used the Voyager ultraviolet spectrometer to make
observations at the beginning and at the end of the Jakobsen et al
scan areas. They obtain only the usual Voyager upper limits. The
interpretation of the differences between the two studies will
appear in upcoming work by Murthy et al
(83). The reason is
either that the Jakobsen et al results are incorrect, or that different
sources are involved at the different wavelengths.

5.7.3 PROGNOZ The Prognoz spacecraft had an orbit that
took it very far from Earth. Solar system L was admitted to the
spectrometer but could be corrected for. The data have been
presented in a number of different forums, and it has been difficult
to follow the details of data selection and treatment. The latest
presentation (119)
shows excellent agreement between some of the
data, and some of the data of Paresce et al
(92).

The authors also point to a possible origin for the
contamination which we suggested above is present in the data of
Paresce et al (91,
92).
The Russian authors refer to a photograph
showing a ``huge cloud of heavy molecules which surrounded the
combined Apollo-Soyuz spaceship and produced strong scattering in
the experiment of Paresce et al
(92)''.

5.7.4 TD - 1 The TD-1 field of view was very
small (1.7 x 10-5 sr),
and time-variable dark current was a serious problem. The TD - 1
data are mentioned here only for reference
(75,
76).